Devices for ionizing residual gases in vacuum systems

ABSTRACT

The disclosed ionizers are of the orbitron type utilizing a high voltage anode in the form of a wire or rod extending axially within an outer generally cylindrical electrode which may be in the form of a cylindrical conductive screen connected to the negative terminal of the power supply. One or more of the ionizers are mounted within a vacuum space containing residual gas molecules to be ionized. The resulting ions may be propelled by electrostatic field forces to the cylindrical screen and also to the walls of the vacuum chamber where the ions may be absorbed or gettered by freshly deposited titanium or some other gettering material. By this mechanism of ion getter pumping, gas molecules are effectively removed from the vacuum space so as to improve the vacuum. In accordance with the present invention, electrons are injected into the space between the axial anode and the outer cylindrical electrode by an electron-emitting electrode which is typically in the form of a generally circular loop or ring encircling the axial anode and spaced inwardly from the cylindrical outer electrode in the radial electric field beween the inner and outer electrodes. The electron-emitting electrode is preferably energized with a direct current which causes heating of the electron-emitting electrode so that electrons are emitted thermionically therefrom. The current also produces an axial magnetic field in the space between the electron-emitting electrode and the anode. The combination of the radial electric field and the axial magnetic field causes a high percentage of the emitted electrons to go into orbits around the anode so that the electrons have extremely long mean-free paths before finally being attracted to the anode. In this way, the orbiting electrons produce a high degree of ionization of the residual gas molecules in the vacuum space. The axial magnetic field may be enhanced by an electromagnet or a permanent magnet disposed near the circular electron-emitting electrode and preferably aligned axially therewith. The electromagnet may take the form of a loop having one or more turns disposed near the electron-emitting electrode or a coil having a multiplicity of turns and preferably having a core of magnetic material. The permanent magnet may be generally cylindrical in shape and disposed axially. The ionizer may also be used to provide an ion gage in which the ion current to the cylindrical electrode is measured.

United States Patent [1 1 Hiller Mar. 12, 1974 DEVICES FOR IONIZINGRESIDUAL GASES 1N VACUUM SYSTEMS Donald Hillel, Deforest, Wis.

[73] Assignee: National Electrostatics Corp.,

Middleton, Wis.

22 Filed: Aug. 21,1972

21 Appl. No.: 282,329

[75] Inventor:

Primary ExaminerL. T. l-Iix [5 7] ABSTRACT The disclosed ionizers are ofthe orbitron type utilizing a high voltage anode in the form of a wireor rod extending axially within an outer generally cylindrical electrodewhich may be in the form of a cylindrical conductive screen connected tothe negative terminal of the power supply. One or more of the ionizersare mounted Within a vacuum space containing residual gas molecules tobe ionized. The resulting ions may be propelled by electrostatic fieldforces to the cylindrical screen and also to the walls of the vacuumcham ber where the ions may be absorbed or gettered by freshly depositedtitanium or some other gettering material. By this mechanism of iongetter pumping, gas molecules are effectively removed from the vacuumspace so as to improve the vacuum. in accordance with the presentinvention, electrons are injected into I the space between the axialanode and the outer cylindrical electrode by an electron-emittingelectrode which is typically in the form of a generally circular loop orring encircling the axial anode and spaced inwardly from the cylindricalouter electrode in the radial electric field beween the inner and outerelectrodes. The electron-emitting electrode is preferably energized witha direct current which causes heating of the electron-emitting electrodeso that electrons are emitted therrnionically therefrom. The currentalso produces an axial magnetic field in the space between theelectron-emitting electrode and the anode. The combination of the radialelectric field and the axial magnetic field causes a high percentage ofthe emitted electrons to go into orbits around the anode so that theelectrons have extremely long mean-free paths before finally beingattracted to the anode. In this way, the orbiting electrons produce ahigh degree of ionization of the residual gas molecules in the vacuumspace. The axial magnetic field may be enhanced by an electromagnet or apermanent magnet disposed near the circular electron-emitting electrodeand preferably aligned axially therewith. The electromagnet may take theform of a loop having one or more turns disposed near theelectron-emitting electrode or a coil having a multiplicity of turns andpreferably having a core of magnetic material. The permanent magnet maybe generally cylindrical in shape and disposed axially. The ionizer mayalso be used to provide an ion gage in which the ion current to thecylindrical electrode is measured.

4 Claims, 18 Drawing Figures PATENIEDMAR 1 2 1974 SHEET 1 OF 4 6 SUPPLYPATENTEUHAR 12 I974 SHEET 2 BF 4 *BIAS LA 0 POWER SUPPLY PATENTEWRZW3.796.917

SHEET 3 BF 4 POWER SUPPLY 0 Powea 3 SUPPLY 3e PATENTEUMR 12 1974 sum uor 4 EXPECTED FILAMENT LIFE (espoouns) (12,000HRs) v p 4 a D 0 3 2 efoDEVICES FOR IONIZING RESIDUAL GASES IN VACUUM SYSTEMS This inventionrelates to ionizers for producing ionization of residual gas moleculesin a vacuum system. Such ionizers are used to produce ion pumping so asto improve the vacuum. In such ion pumping, the ionized gas moleculesare propelled to an electrode or surface where they are absorbed and arepreferably also buried by depositing titanium or some other getteringmaterial on the surface. Such ion getter pumping is especially valuablefor pumping the noble or inert gases such as helium, argon, neon and thelike from the vacuum system.

Such ionizers are also valuable to produce ion gages in which theionized gas molecules are propelled to an electrode so that the ioncurrent can be measured. The ion current decreases as a function of thedecreasing pressure of the residual gases in the vacuum system.

The ionizers of the present invention are of the orbitron type Anionizer of the orbitron type comprises an axial anode, typically in theform of a wire or rod, extending within an outer electrode, typically inthe form of a coaxial cylinder. A positive voltage is applied to theanode relative to the outer electrode so as to produce a radial electricfield therebetween. Electrons are injected into the space between theinner and outer electrodes in such a manner that at least some of themwill go into orbits around the anode. The orbiting electrons willtraverse long paths before finally being attracted to the central anode.The orbitron arrangement makes it possible to increase the mean-freepath of the electrons to a great extent so that the residual gasmolecules in the vacuum space will be ionized to a much greater extentthan would be the case if the electrons were not caused to travel inorbits.

One important object of the present invention is to provide an ionizerof the orbitron type having new and improved means for injecting theelectrons into orbits around the anode so that electrons are injectedinto orbits with significantly greater efficiency, with the result thatmuch greater ionization of the residual gas molecules is produced by theionizer.

Another object is to provide a new and improved ionizer of the foregoingcharacter in which the device for emitting and injecting the electronsis exceptionally rugged and capable of giving extremely long life sothat the useful life of the ionizer will be extended.

A further object is to provide a new ionizer which achieves greatlyimproved freedom from operating instability due to oscillations or thelike.

In accordance with the present invention, the ionizer preferablycomprises a generally cylindrical outer electrode, adapted to beconnected to the negative terminal of the power supply, and an innerelectrode or anode disposed axially within the outer electrode andadapted to be connected to the positive terminal of the power supply sothat a positive potential will be provided be tween the anode and theouter electrode. The ionizer is adapted to be mounted in a vacuum spacecontaining residual gas molecules which are to be ionized. The voltageon the anode produces a radial electric field in the annular spacebetween the anode and the outer electrode. To inject electrons intoorbits around the anode, an electron-emitting electrode is mountedbetween the outer electrode and the anode so as to extend at leastpartially around a circular path encircling the anode and spacedinwardly from the outer electrode.

Typically, the electron-emitting electrode may be in the form ofa loopor ring encircling the anode and disposed in a plane perpendicularthereto. The electronemitting electrode is in the radial electric fieldbetween the anode and the outer electrode. A small positive biasingvoltage may be provided between the electronemitting electrode and thenegatively charged outer electrode.

The ionizer also includes means for producing a general axial magneticfield at the location of the electronemitting electrode. Such magneticfield preferably extends axially in the space between the anode and theelectron-emitting electrode. To produce such axial magnetic field, meansmay be employed to cause an electrical current to flow along theelectron-emitting electrode. Such current may be employed not only toproduce the axial magnetic field, but also to heat the electron-emittingelectrode to such an extent that thermionic emission of electrons willbe produced from the electrode.

A direct current is preferably employed so that the axial magnetic fieldwill be unidirectional and of a steady intensity.

The electrons emitted by the generally circular electrode tend to travelinwardly toward the anode due to the radial electric field. However, theaxial magnetic field imparts curvature to the paths of the electrons sothat a high percentage of the electrons miss the anode and are injectedinto orbits around the anode. The orbiting electrons tend to spiralaxially with a relatively slow axial velocity due to the Coulombrepulsion of the electrons in the space charge produced by the continuous injection of electrons into orbits.

The axial magnetic field may also be produced or enhanced by anelectromagnet or a permanent magnet positioned in the vicinity of theelectron-emitting electrode. The electromagnet may take the form of asingle loop or turn adapted to carry a magnetizing current andpreferably coaxial and coplanar with the electron emitting electrode.Alternatively, the electro-magnet may comprise a multi-turn coil,aligned axially with the electron-emitting electrode and preferablyprovided wih a core made of a magnetic material.

The axial magnetic field may be produced by a generally cylindricalpermanent magnet axially aligned with the electron-emitting electrode.If an electromagnet or a permanent magnet of sufficient strength isemployed, the electron-emitting electrode may be heated by the use ofalternating current.

The circular electron-emitting electrode may be rugged and may beoperated at a relatively low tempera ture so that it will provideextremely long operating life.

Further objects, advantages and features of the present invention willappear from the following description, taken with the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic elevational view of an ionizer to be describedas an illustrative embodiment of the present invention.

FIG. 2 is a longitudinal section taken generally along the line 22 inFIG. 1.

FIG. 3 is a transverse section taken generally along the line 33 in FIG.2.

FIG. 4 is an elevational view similar to FIG. 1 but showing a modifiedionizer.

FIG. 5 is a transverse section taken generally along the line 55 in FIG.4.

FIG. 6 is an enlarged diagrammatic longitudinal section through theionizer of FIGS. 4 and 5 and showing the electric and magnetic fieldsaround the electronemitting electrode.

FIG. 7 is a diagrammatic transverse section through the ionizer of FIG.6 and illustrating the manner in which the electrons are injected intoorbits.

FIG. 8 is a fragmentary elevation, similar to FIG. I, but showinganother modified construction utilizing a singleturn loop to enhance theaxial magnetic field.

FIG. 9 is a fragmentary longitudinal section taken generally along theline 99 in FIG. 8.

FIG. 10 is a diagrammatic transverse section taken generally along theline ll010 in FIG. 9.

FIG. 11 is a fragmentary elevation, similar to FIG. 8, but illustratinganother modified construction utilizing an electromagnet to produce orenhance the axial magnetic field.

FIG. 12 is a fragmentary longitudinal section taken generally along theline l.212 in FIG. 11.

FIG. 13 is a transverse section taken generally along the line 1313 inFIG. 12.

FIG. 14 is a fragmentary elevation similar to FIG. 1, but showinganother modified construction utilizing a permanent magnet to produce orenhance the axial magnetic field.

FIG. 15 is a fragmentary longitudinal section taken generally along theline l5l5 in FIG. 14.

FIG. 16 is a transverse section taken generally along the line l616 inFIG. 15.

FIG. 17 is a diagrammatic perspective view showing a getter-ion vacuumpump utilizing the ionizers of the present invention.

FIG. 18 is a graph illustrating the pumping characteristics of agetter-ion pump utilizing one of the ionizers of the present invention.

More detailed consideration will now be given to FIGS. l3 whichillustrate an ionizer 20 adapted to be employed to ionize residual gasmolecules in a vacuum space. One possible application of the ionizer 20is shown in FIG. 17 which illustrates a getter-ion vacuum pump 22 forpumping residual gas molecules from a vacuum space 24 within a casing26.

The getter-ion pump 22 comprises a plurality of the ionizers 20,although a single ionizer could be employed. The use of a plurality ofionizers increases the pumping rate which can be achieved by the pump22. As shown, the pump 22 utilizes eight of the ionizers 20.

The getter-ion pump 22 of FIG. 17 also employs one or more devices 28for evaporating or subliming titanium or some other gettering material,which is condensed or deposited upon the inside of the casing 26 and iseffective to absorb gas molecules so that they are effectively removedfrom the vacuum space 24. The ionizers 20 are employed to ionize the gasmolecules so that they will be propelled by electrostatic forces to theinside of the casing 26 where the ions are neutralized and absorbed bythe getter material. The neutral gas molecules are buried by theprogressive deposition of the getter material.

Each of the getter-subliming devices 28 may comprise a body 30 oftitanium or some other getter material, together with means for heatingthe body 30 so that the getter material will be sublimed or evaporated.

As shown, the body 30 of getter material is adapted to be heated by anelectrical heating element 32 mounted within or adjacent the body 30. Asshown, the titanium body 30 is in the form ofa hollow cylinder withinwhich the electrical heating element 32 is mounted.

While a single titanium sublimer 28 would produce a pumping action, itis preferred to employ a plurality of sublimers within the casing 26 toprovide a greater pumping capacity and to prolong the life of the pumpby providing a larger quantity of titanium which can be sublimed tomaintain the pumping action. It is preferred to bring a plurality ofleads 34 out of the casing 26 to an external power supply 36 so thateach of the heating elements 32 can be energized individually. In thisway, one or more of the sublimers 28 can be energized according to thedesired pumping capacity. Either direct or alternating current may beemployed to energize the heating elements 32 of the sublimers 28, butalternating current is generally preferred because it can be suppliedmore easily and economically.

In FIGS. 13, the casing which forms the walls of the vacuum system isnot shown, but it will be understood that the ionizer 20 is adapted tobe operated in a vacuum space.

As previously indicated, the ionizer 20 is of the orbitron type having acentral anode 4t), typically in the form of a wire or rod which extendsaxially within an outer electrode 42, typically in the form of a hollowconductive cylinder. However, the outer electrode 42 need not becylindrical in shape just so long as the outer electrode extends aroundthe inner electrode or anode 40 so that an approximately radial field isproduced between the anode 40 and the outer electrode 42 when a positivevoltage is applied between the anode and the outer electrode.

As shown in FIG. 1, the positive voltage is provided by an external highvotlage supply 44. Leads 46 and 48 are brought out of the vacuum spaceto the positive and negative terminals of the high voltage supply fromthe anode 40 and the outer electrode 42. A meter 50 may be connected inseries with the outer electrode lead 48 to measure the ion current tothe outer electrode 42. Such ion current provides an indication of theresidual gas pressure in the vacuum space. Thus, the ionize may beutilized as an ion gage.

Forion pumping applications, the anode voltage provided by the highvoltage supply 44 is typically quite high, up to about 10 kilovolts, forexample. However, the voltage may be varied widely according to thedesired pumping capacity. For small pumps, the anode voltage may be onlya few kilovolts, for example. When the ionizer is used as an ion gage,the anode voltage is typically quite low, amounting to only a fewhundred volts, for example.

The outer cylindrical electrode 42 may be in the form of a solidconductive wall made of sheet metal or the like, but is preferably inthe form of a cylindrical screen or mesh as illustrated in FIG. 1. Thecylindrical mesh permits most of the positively charged gas ions totravel outwardly through the mesh without being intercepted so that theions will continue to travel outwardly to the outer walls of the casing26 where the ions will be ab sorbed and buried by the getter material asexplained above in connection with FIG. 7.

The illustrated anode 40 is in the form of a wire stretched between twosprings or resilient supports 52 mounted on insulators 54. The anodewire 40 extends through axial openings 56 in a pair of end plates 58 atthe opposite ends of the outer cylindrical electrode 42. As shown, thecylindrical electrode 42 is connected to the end plates 58 so that theend plates are at the same electrical potential as the outer electrode42. However, the end plates 58 could be insulated from the outerelectrode 42 and maintained at a somewhat different potential, ifdesired.

The ionizer is provided with means for injecting electrons into theradial electric field between the anode 40 and the outer electrode 42 insuch a manner that many of the electrons will go into orbits around theanode. In accordance with the present invention, such means may take theform of an electron-emitting electrode 60 disposed between the anode 40and the outer electrode 42. The electron-emitting electrode 60preferably extends at least part way around a generally circular pathencircling the anode 40 and spaced inwardly from the outer electrode 42.

FIG. 3 illustrates on typical form of the electronemitting electrode 60.It will be seen that the electrode 60 is in the form of a generallycircular loop or ring constituting a one-turn coil and having its endsconnected to supporting leads 62 and 64. One or more insulators 66 areprovided to mount the leads 62 and 64 on one of the end plates 58. Theloop electrode 60 is in a plane perpendicular to the central anode 40which extends axially through the loop 60. The electron emittngelectrode 60 may be mounted anywhere along the length of the anode 40between the end plates 58, but preferably not 'too close to the endplates so that the electrode 60 will be in a substantially radialelectric field.

The ionizer 20 is also provided with means for producing an axialmagnetic field in the vicinity of the electron-emitting electrode 60.Preferably, the magnetic field extends in a generally axial directionthrough the plane of the electrode 60. In the ionizer 20 of FIG. 1, theaxial magnetic field is produced by causing an electrical current toflow around the loop electrode 60 which acts as a single'turn coil. FIG.2 includes a diagrammatic illustration of the magnetic lines of force 68produced by the current flowing along the circular electrode 60.

The electrons emitted by the generally circular electron-emittingelectrode 60 are attracted inwardly toward the positively charged anode40.. Due to the axial magnetic field produced by the current in theelectrode 60, the inward paths of the electrons are given a curvaturewhich causes them to miss the anode 40 so that many of the electrons areinjected into orbits around the anode.

The action of the axial magnetic field may also be explained by notingthat the magnetic field applies a lateral force to the electrons as theytravel inwardly toward the axial anode. Such lateral force isperpendicular to both the radial and axial directions. Thus, the lateralforce imparts angular momentum to the electrons. Such angular momentumis conserved as the electrons travel in the radial electric field whichexists between the coaxial electrodes 40 and 42. Thus, the electronstend to travel through many orbits around the axial anode 40 before theyeventually are attracted to the axial anode. Some of the orbitingelectrons collide with gas molecules or encounter them in such a manneras to cause ionization of the gas molecules. Due to the orbiting of theelectrons, they have an extremely long mean-free path so that theprobability of a particular electron causing ionization of a gasmolecule is greatly increased. Thus, the orbiting of the electronsgreatly increases the total ionization of the gas molecules.

The magnetizing current in the circular electrode 60 also causes heatingof the electrode. While the electrode 60 may be heated by other means,it is preferred to regulate the current through the electrode so that itis heated sufficiently to produce copious thermionic emission ofelectrons. Thus, the circular electrode 60 preferably comprises both athermionic filament for emitting electrons and a single-tum coil forproducing an axial magnetic field.

As shown in FIG. 3, leads 70 and 72 are preferably brought out of thevacuum space from the supports 62 and 64 for the circular filament 60 toan energizing circuit comprising a power supply 74. As shown, a vari'able resistor 76 and an ammeter 78 are connected in series with thepower supply 74 and the filament 60, so that the filament current can beadjusted to any desired value. The power supply 74 preferably suppliesdirect current so that the axial magnetic field will be unidirectionaland constant in intensity.

The electron-emitting electrode 60 may be operated at the potential ofthe outer electrode 42, which is usually at ground potential. However,it is preferred to bias the electrode 60 to a potential which is greaterthan the potential of the outer electrode 42, but much less than thepositive potential on the anode 40. Thus, for example, for an anodepotential of l0 kilovolts, the electronemitting electrode 60 may bebiased to a positive potential of a few hundred volts.

As shown in FIG. 1, the biasing potential for the electron-emittingelectrode 60 is provided by a bias voltage supply 80 having its negativeoutput terminal connected to the negative terminal of the high voltagesupply 44. To provide for adjustment of the biasing potential, apotentiometer 82 is connected between the positive and negative outputterminals of the bias voltage supply 80. The potentiometer 82 has amovable contact 84 which is connected by means of a lead 86 to one sideof the electron-emitting electrode 60.

In operation, the electron-emitting electrode 66 is heated by energizingthe filament power supply 74 so that a direct current will flow alongthe electrode 60. In this way, the electrode 60 is heated to asufficiently high temperature to cause the thermionic emission ofelectrons. The high voltage supply 44 is energized so that a positivepotential ranging up to about 10 kilovolts is applied to the anode 40relative to the outer electrode 42, which usually is at groundpotential. The bias voltage supply 80 is also energized so that a muchsmaller positive biasing voltage is applied to the electron-emittingelectrode 60. The potentiometer 82 may be adjusted to vary the biasingvoltage.

The direct current which flows around the circular electrode 60 producesan axial magnetic field in the vicinity of the electrode andparticularly between the electrode 60 and the anode 40. Thethermionicallyemitted electrons are attracted inwardly toward the anode4G by the radial electric field due to the positive anode potential.However, the axial magnetic field imparts curvature to the paths of theelectrons so that many of them miss the anode 40 and go into orbitsaround the anode. Thus, the electrons pick up angular momentum due tothe force exerted on the electrons by the magnetic field.

FIG. 6 constitutes a diagrammatic illustration of the radial electricfield between the anode 40 and the outer electrode 42. FIG. 6 alsoillustrates the magnetic lines of force 68 produced by the directcurrent flowing around the loop-shaped electrode 60. It will be seenthat the magnetic lines of force 68 extend axially in the plane of theelectrode 60.

FIG. 7 illustrates a sample orbit 88 of one of the electrons emittedinto the radial electric field and the axial magnetic field by theelectrode 60. Generally, the orbits are approximately eliptical ratherthan circular in shape.

Due to the continuous emission of electrons by the circular electrode60, a space charge of electrons is developed in the vicinity of theelectrode 60. By Coulomb repulsion, the space charge causes the orbitingelectrons to spiral or drift slowly along the length of the anode 40 sothat gradually the orbiting electrons occupy the entire space betweenthe anode 40 and the outer electrode 42. The spiraling electrons tend tobe reflected axially by the end plates 58 so that the electrons arecaused to drift in the opposite axial direction along the anode 40.

Some of the orbiting electrons collide with residual gas molecules orcome into close enough proximity to the gas molecules to causeionization thereof. The positive gas ions are attracted outwardly towardthe outer electrode 42 by the electric field between the electrodes 40and 42. Some of the positive gas ions impinge upon the outer electrode42 whereupon the electric charges of the ions are neutralized. Theresulting ion current is measured by the meter 50. Some of the gas ionsare absorbed by the outer electrode 42, which may be made of or coatedwith a gettering material, such as titanium, for example.

In the vacuum pump 22 of FIG. 17, the getter material is condensed ordeposited upon the outer electrode 42 so that some of the gas moleculestend to be buried by the freshly deposited getter material.

Due to the open mesh construction of the outer electrode 42, most of thepositive gas ions travel outwardly through the openings in the screenelectrode 42 and continue to travel outwardly until the gas ions impingeupon the outer wall of the casing 26. Generally, the easing 26 and theouter electrode 42 are at the same potential. Typically, both are atground potential. The ions which strike the inner wall of the casing 26are absorbed and buried by the titanium or other getter material, whichis condensed or deposited on the inside of the casing 26 after beingvaporized by one or more of the subliming devices 28.

The circular electron-emitting electrode or filament 60 is rugged inconstruction so that it gives a long operating life.

FIGS. 4 and illustrate a modified ionizer 90 which is similar to theionizer of FIG. 1, except that the electron-emitting electrode orfilament 60 is located centrally between the end plates 58 rather thanbeing disposed relatively close to one of the end plates as in FIG. 1.Actually, the electrode 60 may be located any where along the axis ofthe ionizer 90. The electrode 60 produces its own axial magnetic fielddue to the current which is employed to energize the electrode. Thus,the magnetic field is present regardless of the position of theelectrode 60.

Due to the central position of the electrode 60 in FIG. 4, the electrodehas relatively long supports 92 and 94 in the form of stiff conductivewires or rods. It will be seen that the supports 92 and 94 extend intothe space within the outer electrode 42 through an opening 96 therein.The ionizer may be supplied with energizing voltages in the same manneras illustrated in FIGS. l-3.

In the operation of the ionizer 90, electrons are injected into orbitsin the same manner as described in connection with FIGS. 1-3. Theorbiting electrons produce a space charge in the vicinity of theelectrode 60. By Coulumb repulsion, the space charge causes the orbitingelectrons to spiral or drift gradually along the axis of the ionizer 90in both directions from the electrode 60. At the end plates 58, theaxial movement of the orbiting electrons is reversed so that theelectsons can continue to travel in orbits around the anode 40.

In FIG. 6, the electron-emitting electrode is shown in a centrallocation along the axial anode 40, but the diagrammatic illustration ofthe electric and magnetic fields is applicable to FIGS. l-3 as well asFIGS. 4 and 5 In both FIGS. 6 and 7, the distribution of the electricfield is represented by a series of cylindrical equipotential surfacesdesigna ted )1 1 V0, 0.2 V015 V where V0 is the anode voltage. Severalof the magnetic lines of force 68 are also shown in FIG. 6 as previouslyindicated.

FIGS. 8l(l illustrate another modified ionizer 100, which is similar tothe ionizer of FIG. 1, except that the magnetic field produced by thecircular electronemitting electrode 60 is enhanced by an elementaryelectromagnet in the form of a Single conductive loop or turn 102disposed in the vicinity of the electronemitting electrode 60. As shown,the loop 102 is coaxial and coplanar with the electrode 60. Preferably,the loop 102 is spaced outwardly from the electronemitting electrode 60.The loop 102 may be made of wire which is heavy enough to be rigid andselfsupporting, Inasmuch as the loop 102 does not need to be heated,there is no particular advantage in making it out of fine wire.

The ionizer 100 is provided with means for causing a current to flowaround the loop 102 so that it will produce an axial magnetic field.Direct current is preferably employed so that the field will be constantand unidirectional.

The same current which heats the electrode 60 may be caused to flowaround the loop 102 so that the magnetic field produced by the currentin the electrode 60 will be enhanced by the additional turn provided bythe loop 102. As shown in FIG. 10, the loop 102 is connected in serieswith the electron-emitting-electrode 60. Leads 104 and 106 are broughtout of the vacuum space from the ends of the loop 102 so that the seriesconnection can be made externally.

The electrode 60 and the loop 102 are connected in series across adirect current power supply 108. In order to provide for adjustment ofthe current, a variable resistor 110 may also be connected in serieswith the power supply 108. Any other suitable regulating arrangement maybe employed.

The circuit of FIG. 10 also includes ammeters 112 and 114 in series withthe electrode 60 and the loop 102, as well as variable resistors 116 and118 connected in parallel with the electrode 60 and the loop 102. Thevariable resistors 116 and 118 make it possible to regulate the currentsthrough the electrode 60 and the loop 102 separately. In this way, theheating current through the electrode 60 can be adjusted to achieve thedesired emission of electrons. The magnetic field can then be adjustedby changing the current through the loop 102. If desired, independentpower supplies may be provided for the electrode 60 and the loop 102.

FIGS. 1113 illustrate another modified ionizer 102, which is similar tothe ionizer of FIGS. 1-3, except that an electromagnet 122 is providedto enhance the axial magnetic field in the vicinity of theelectronemitting electrode 60. In this case, the electromagnet 122comprises a solenoid or coil 124 having a plurality of turns.Preferably, the electromagnet 122 has a core or pole-piece 126 withinthe coil 124. The core 126 may be made of iron or some other magneticmaterial having high permeability.

The illustrated core 126 is in the form ofa hollow cylinder arranged toencircle the anode 40. The coil 124 and the core 126 are preferablycoaxial with the anode 40 and are located as close as possible to theelectronemitting electrode 60. Much of the axial magnetic field producedby the electro-magnet 122 extends through the loop-shaped electrode 60.

In the arrangement of FIGS. 11-13, the electronemitting electrode 60 andthe electromagnet 122 have separate power supplies 128 and 130. Theelectromagnet 122 is preferably energized with direct current so thatthe axial magnetic field will be constant and unidirectional. As shown,the potentiometer 132 is provided between the power supply 130 and theelectromagnet 122 to regulate the energization of the electromagnet sothat the magnetic field can be varied.

The power supply 128 for the electron-emitting electrode or filament 60may provide either direct or alternating current. The use of directcurrent will make it possible to enhance the axial magnetic field, butsuch enhancement is not necessary because the electromagnet 122 iscapable of producing an intense magnetic field. The filament powersupply 128 may utilize any suitable device for adjusting the filamentcurrent.

FIGS. 14-16 illustrate still another modified ionizer 140, which issimilar to the ionizer 120 of FIGS. 11-13, except that a permanentmagnet 142 is employed rather than the electromagnet 122 to produce orenhance the axial magnetic field. The position of the permanent magnet142 is similar to that of the magnetic core 126. Thus, the illustratedpermanent magnet 142 is in the form of a hollow cylinder coaxial withthe anode 40 and positioned on the opposite side of the end plate 58from the electron-emitting electrode 60. Due to the closeness of thepermanent magnet 142 to the electrode 60, much of the magnetic field ofthe permanent magnet extends through the loop-shaped electrode 60.

The permanent magnet 142 is capable of producing a strongelectromagnetic field regardless of the current which may be flowingalong the electrode 60. Here again, the electrode 60 may be energizedwith either alternating or direct current. If direct current isemployed, the polarity of the magnetic field produced by the directcurrent should be the same as the magnetic polarity of the permanentmagnet 142.

The circular electron-emitting electrode or filament 60 has theadvantage of producing high emission of electrons and high injectionefficiency so that a high percentage of the emitted electrons areinjected into stable orbits around the anode 40. In this way, theelectrons have an extremely long mean-free path so that the ionizerproduces a high level of ionization. Thus, the ionizer produces a highpumping rate when employed in a getter-ion pump of the general typerepresented by FIG. 17. Moreover, the circular filament is rugged and iscapable of providing long filament life.

FIG. 18 is a graph in which the argon pumping speed, in liters persecond, is plotted along the Y axis against filament current, inalternating current amperes, plotted along the X axis. The graphrepresents the performance of a simple getter-ion pump, similar to thatof FIG. 17, but having only a single ionizer and a single tita niumsublimer.

It will be seen that in this particular pump the argon pumping speedincreased rapidly with increasing filament current up to algnee or bendinthecurve between 9 and 10 amperes. The pumping speed then increasedmuch less rapidly with increasing filament current. By operating thepump approximately at the knee of the curve, a high pumping speed can beachieved while also providing long filament life. The approximatefilament life to be expected for various filament currents is alsoindicated along the X axis in FIG. 18. It will be seen that the filamentcan be expected to give a life in excess of 65,000 hours when operatedat the knee of the curve where the filament current is about 9.5amperes,

I claim:

1. An ionizer for ionizing residual gas molecules in a vacuum space,

comprising a hollow generally cylindrical outer electrode,

an inner electrode disposed axially within said outer electrode andadapted to be charged with a positive potential with respect to saidouter electrode to produce a radial electric field in the annular spacebetween said inner and outer electrodes,

a generally circular electron-emitting loop electrode extending aroundsaid inner electrode and spaced radially inwardly from one end portionof said outer electrode,

said loop electrode being generally coaxial with said inner electrodeand being disposed near one end thereof,

and a generally cylindrical permanent magnet substantially coaxial withsaid loop electrode,

said permanent magnet having an outside diameter less than the diameterof said outer electrode and having one end closely spaced axially fromsaid electron-emitting loop electrode in an end-to-end confrontingrelationship thereto for producing a generally axial magnetic fieldadjacent said electron-emitting loop electrode and in the space betweensaid electron-emitting loop electrode and said inner electrode to impartcurvature to the paths of the electrons emitted by said electronemittingloop electrode whereby the electrons will be injected with highefficiency into orbits around said inner electrode.

2. An ionizer according to claim 1.,

in which said generally cylindrical permanent magnet is ring-shaped andhas an axially disposed generally cylindrical opening through which saidinner electrode extends,

said opening being larger in diameter than said inner electrode butsmaller in diameter than said electron-emitting loop electrode.

3. An ionizer for ionizing residual gas moleculdes in a vacuum space,

comprising a hollow generally cylindrical outer electrode,

an inner electrode disposed axially within said outer electrode andadapted to be charged with a positive potential with respect to saidouter electrode to produce a radial electric field in the annular spacebetween said inner and outer electrodes,

21 generally circular electron-emitting loop electrode extending aroundsaid inner electrode and spaced radially inwardly from one end portionof said outer electrode,

said loop electrode being generally coaxial with said inner electrodeand being disposed near one end thereof,

and an electromagnet having a coil with a generally cylindrical coresubstantially coaxial with said loop electrode,

said core having an outside diameter less than the diameter of saidouter electrode and having one end closely spaced axially from saidelectron-emitting loop electrode in an end-to-end confrontingrelationship thereto for producing a generally axial magnetic fieldadjacent said electron-emitting loop electrode and in the space betweensaid electronemitting loop electrode and said inner electrode to impartcurvature to the paths of the electrons emitted by saidelectron-emitting loop electrode whereby the electrons will be injectedwith high efficiency into orbits around said inner electrode.

4. An ionizer according to claim 3,

in which said generally cylindrical core is ring-shaped and has anaxially disposed generally cylindrical opening through which said innerelectrode extends,

said opening being larger in diameter than said inner electrode butsmaller in diameter than said electron-emitting loop electrode.

1. An ionizer for ionizing residual gas molecules in a vacuum space,comprising a hollow generally cylindrical outer electrode, an innerelectrode disposed axially within said outer electrode and adapted to becharged with a positive potential with respect to said outer electrodeto produce a radial electric field in the annular space between saidinner and outer electrodes, a generally circular electron-emitting loopelectrode extending around said inner electrode and spaced radiallyinwardly from one end portion of said outer electrode, said loopelectrode being generally coaxial with said inner electrode and beingdisposed near one end thereof, and a generally cylindrical permanentmagnet substantially coaxial with said Loop electrode, said permanentmagnet having an outside diameter less than the diameter of said outerelectrode and having one end closely spaced axially from saidelectron-emitting loop electrode in an end-to-end confrontingrelationship thereto for producing a generally axial magnetic fieldadjacent said electron-emitting loop electrode and in the space betweensaid electron-emitting loop electrode and said inner electrode to impartcurvature to the paths of the electrons emitted by saidelectron-emitting loop electrode whereby the electrons will be injectedwith high efficiency into orbits around said inner electrode.
 2. Anionizer according to claim 1, in which said generally cylindricalpermanent magnet is ring-shaped and has an axially disposed generallycylindrical opening through which said inner electrode extends, saidopening being larger in diameter than said inner electrode but smallerin diameter than said electron-emitting loop electrode.
 3. An ionizerfor ionizing residual gas moleculdes in a vacuum space, comprising ahollow generally cylindrical outer electrode, an inner electrodedisposed axially within said outer electrode and adapted to be chargedwith a positive potential with respect to said outer electrode toproduce a radial electric field in the annular space between said innerand outer electrodes, a generally circular electron-emitting loopelectrode extending around said inner electrode and spaced radiallyinwardly from one end portion of said outer electrode, said loopelectrode being generally coaxial with said inner electrode and beingdisposed near one end thereof, and an electromagnet having a coil with agenerally cylindrical core substantially coaxial with said loopelectrode, said core having an outside diameter less than the diameterof said outer electrode and having one end closely spaced axially fromsaid electron-emitting loop electrode in an end-to-end confrontingrelationship thereto for producing a generally axial magnetic fieldadjacent said electron-emitting loop electrode and in the space betweensaid electron-emitting loop electrode and said inner electrode to impartcurvature to the paths of the electrons emitted by saidelectron-emitting loop electrode whereby the electrons will be injectedwith high efficiency into orbits around said inner electrode.
 4. Anionizer according to claim 3, in which said generally cylindrical coreis ring-shaped and has an axially disposed generally cylindrical openingthrough which said inner electrode extends, said opening being larger indiameter than said inner electrode but smaller in diameter than saidelectron-emitting loop electrode.